Production of akomatic



April 28, 1953 A. e. OBLAD ETAL PRODUCTION OF AROMATIC HYDROCARBONS Filed Dec. 26, 1951 INVENTORS H1 EX l1. [111L311 BE: nrg a QMiHE BY Patented Apr. 28, 1953 PRODUCTION OF AROMATIC HYDROCARBONS Alex G. @blad, Springfield, and George Alexander Mills, Swarthmore, Pa., assignors to Houdry Process Corporation, Wilmington, DclL, a corporation of Delaware Application December 26, 1951, Serial No. 263,322

9 Claims. l

The present invention relates to the productlon and recovery of aromatic hydrocarbons from a naphtha charge and is particularly concerned with improvements in operation of the process whereby the reaction products obtained include desired yields of aromatics, such as, benzene, toluene and xylenes, the reaction products being in a form such that they are readily separable by distillation to recover toluene of relatively high purity.

in known procedures for the production. of desired aromatic hydrocarbons of substantial purity from petroleum, it has been the practice to treat only a very narrow fraction of the naphtha, rich in the component or components capable of being converted to the desired aromatic hydrocarbon. Thus, for the production of toluene, a naphtha cut of 200250 F. boiling range and rich in methyl cyclohexane is charged to dehydrogenation. Often to obtain desired yields the hydrocarbon material charged is specially prepared; for instance, one or more dimethyl cyclopentane fractions are isomerized to produce methyl cyclohexane which is added to the methyl cyclohexane cut from the original naphtha to provide the charge for dehydrogenation. If other aromatic. hydrocarbons are also to be produced by such separately blocked out operations, the process becomes cumbersome and expensive from the standpoint of additional equipment requirements.

By the present invention a novel method is provided whereby a selected naphtha fraction is reformed to convert C7 naphthenes therein to toluene, while other components of the charge are simultaneously converted to aromatic hydrocarbons such as benzene and xylene, and the toluene cut distilled from the reformate is composed of toluene of relatively high purity; that is, in a form substantially uncontaminated by other hydrocarbons of approximately the same boiling point as toluene. This desirable result is achieved in accordance with the invention by distilling a naphtha fraction having a boiling range to include components from methyl cyclopentane through dimethylcyclohexane, to remove a heart out of materials boiling within about 10 (F.) above and below toluene and comprising parafiins which would pass through the reforming process largely in unconverted form, or at least in noncyclicized form. The remaining naphtha, free of the heart out, is then subjected to a step of dehydrogenation and reforming, the products of which step are distilled and a middle fraction boiling approximately in the range of 220-240 F. recovered, which cut will containv 2 toluene in a state of fairly high purity. In the products boiling above and below this range a Xylenes fraction and a benzene fraction, respectively, are separated.

The details of the process will be understood from the description which follows read in confor instance, that cut boiling in the range of 220- 240 F. For example, in the still I i the naphtha is separated into a light fraction boiling up to about 220 F. and a heavy fraction boiling above about 220 IE2, the latter being sent to still E2 to separate out therefrom lower-boiling material as an overhead fraction boiling for instance up to 240 F. The light fraction from still i l is taken off overhead through line I3 and together with the higher boiling materials removed from still l2 by line It is heated to required temperature by being passed through heater :5 and sent to the reforming step carried out in a suitable pressurized converter Hi, to which hydrogen or a hydrogen-rich gas is also admitted, supplied by line H. The efiluent from the reforming step is suitably cooled (l8) and sent to a gas separator [9 wherein the condensed liquid components of the charge are separated from the fixed lower boiling point gases. The latter are withdrawn by a line 20 and the hydrogen-rich gas stream recycled to the reforming step carried out in converter 16. Preferably the gas and vapors in line 29 are further purified by being passed through a scrubber 2! to remove the major portion of the light hydrocarbon gases, in known manner, as by use of a suitable scrubbing liquid supplied through line 22.

The condensed liquid from the gas separator is sent by a line 23 to still 2 4 for separation into an overhead benzene cut boiling up to about 220 F. and a cut boiling above 220 F. withdrawn through line 25. The higher boiling cut is sent to a still 26 wherein it is separated into a toluene fraction containing the materials boiling over the range of 220-240 F. and a xylene fraction comprising the materials boiling above 240 F. The overhead from still 26 withdrawn through line .21 mayhave an average toluene concentration or? about 85%. Toluene of higher purity can be obtained in the efiluent from still 28 by operating that still on separate batches of the 220 F.+ material from still 24 and separately collecting that portion of the overhead from still 23 constituting approximately the middle portion of the 220-2 F, boiling range material, for example that boiling at between 230-235" Or, if desired, the entire 220-240" F. fraction from still 26 may be redistilled and the toluene collected in a state of higher purity. The higher boiling materials from still 25, constituting the xylene fraction, are withdrawn through line 2.8 may be further separated and/or purified in known or desired manner, or may be employed as such, in the blending of gasoline or the preparation of industrial products. LikeWise the benzene-containing cut from still 24 is withdrawn through line 29 and may be further fractionated and/or treated to recover benzeneof desired purity. For instance, the benzene-containing. cut or any desired. distillate thereof may be subjected to seleotiveextraction of the aromatics, for instance by chromatographic adsorptionon silica gel. The invention is not limited to any particular method of treating, or pu'ifying the benzene fraction or.

the xylene fraction, details of onesuitable method of operation employing an adsorption-desorption technique for recovery ofaromatics are described in Olsen, U. S. 2,564,717, issued August 21,

The 22ue-2 lD'F. .cut taken out in still i2 constitutes but a minor'part of the-initial naphtha charge ac-235 11), ordinarily less than about 10-15%therecf; and maycontain a small amount of toluene. F. materials sep-aratedin still I 2 from the hydrocarbons chargedto converter It may appear to represent some slight'loss in possible toluene re,- covery, such exclusion is more than compensated by the improved purity of the obtained toluene fraction recoverable. without substantial loss in yield by simple distillation of the reformate. It will be'understood, of course, that the toluene content of the 220-24; 0F; fraction separated in still. i2 may be'separately recovered, if'desired.

The various cuts from distillation which are not-directly'en'lployed in the recovery of the desired benzene, toluene and xylene fractions are suitable for use as'gasoline blending products or in other industrial applications requiring hydIOChIDOIlS." This applies, for instance, to the 220-240 cut iroin still i2 as well todistillates that may be obtained by redistiilation of the benzene out in line 2 c.

The reforming step in converter is ispreferably operated under conditions favoring'the clehydrogenation of C6 ringnaphthenes accompa nied by the dehydroeisoznerization of alkyl cyclopentanes. The reforming operation is carried out at temperatures in the order of 350-1050" F. and pressures of from about 10-49 atmospheres, hydrogen being added'tothe charge in a qua n tity providing 1-10 mols per incl ofhydrocarbon; space rates offrom about i to lo volumes of hydrocarbon per hour per volume of catalyst may be employed.

It has also been found that in the conversion of cyclohe zane and/ormethylcyclopentane to benzene over noble metalfcatalyst the pressure employed in the op ration has a pronounced effect on the aromatics yield whereas in the case of forming toluene from methylcyclohexane or olimethylcyclopentane the efic'ct of pressure'while in the same direction is considerably-less important. Accordingly, in" the preferred operationof the reforming. steps employedin, the present procs While the exclusion of "the 220-bit) ess when charging a naphtha distillate containing both benzene-forming and toluene-forming naphthenes, the pressure conditions are selected to favor good benzene yields. While progressive decrease in total pressure from about 800 to about 1.00 or pounds per square inch results in increased benzene production, such pressure reduction also favors side reactions leading to coke build up, so that for a continuous non-regenerative process the selection of operating pressure should be. accordingly limited. At an operating pressure of from about 250 to 400 pounds per square inch (gauge) good yields of both benzene and toluei e are obtained without significant coke format-ion.

The preferred catalysts for the process are of the noble metal type, particularly supported platinum, the supporting carrier being one which has a high surface area and preferably little or no catalytic activity as such, for promoting carbon-carbon scission or polymerization. Suitable supports include activated alumina which has been leached with a mild acid, such as acetic acid; alumina which has been pie-treated with alkali earth metal oxide, for instance, that incorporating to 5% MgO'; and magnesia itself as a support. Only a relatively small amount of platinum is incorporated in the carrier as from about 0.05 to 2% by weight thereof, preferably more of the original naphtha charged to the,

still, contains principally parafiins, and harm:

therles in varying amounts depending upon the source of the naphtha, and perhaps a small amountv of aromatics in the order of about 5% oi" the cut; The Caring naphthenes, including cyclohexane and methylcyclohexane, are.

substantially completely dehyd-rogenated to hen,- zone and toluene respectively, while the Caring naphthenes, including methylcyclopentane and ciimethylcyclopentane, are also largely converted to corresponding aromatic through dehydroisomerization. Parafiinsin the cut passthrough.

higher aromatics content than the lighter boiling out. The parafiinswhich are mostly of theGa.

type pass through largely unchanged while the naphthenes are converted to xylenes. The 225 240 F, heart out which is not charged to the reforming step containsparafilns boiling in therange of toluene and some naphthenes chiefly of the,trimethylcyclopentane type.

Example A straight run light naphtha boiling in the range-of 150-270. F. wasifractionated' into (1) an, overheadcutboiling up to 220? and comprising about 55 volume-per cent ofthe naphtha,

(2) a middle cut boilin' in the range of 220-240 F. andcomprising about 15 volume percent, and

cent. Themidolle out being removed, the overhead'and bottoms fractions were charged to re-- forming over a catalyst. comprising 0.5 platinum. on activatedalumina which had been pre.-

viously leachedwithiaceticacid, operating at a pressure. of. 3.00. pounds; per. square inch at"950 .5 FE, and at a space rate of 2 volumes of naphtha per hour per volume of catalyst; 3 mols of hydrogen being charged per mol of naphtha. Approximately 98% of the total naphthenes present were converted to aromatics but the parafiines remained substantially unchanged.

By distillation of the reformate and collecting the fraction boiling between about 220-2-i0 R, toluene of about 85% purity is recovered, from which by redistillation toluene of 90-95% purity is obtained.

It will be understood of course, that the apparatus arrangement shown in the accompanying drawing is merely illustrative and that the operation of the process of the invention is not dependent thereon. For instance, the equipment requirements can be considerably simplified by resorting to batch or partial batch operation, and a single still can be used alternately for the various fractionating operations described, suitable provision being made for interim storage of collected products.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

l. The method of converting C7 naphthenes in a naphtha charge to toluene with the simultaneous production of at least one aromatic hydrocarbon compound from the group consisting of benzene and xylenes, which method comprises: distilling a naphtha fraction of suitable boiling range to remove therefrom components boiling within 10 F. of toluene, reforming the remaining naphtha under dehydrogenating conditions eifective at least to aromatize methyl cyclohexane, distilling the resulting reformate and recovering a toluene-containing distillate of narrow boiling range.

2. The method of producing toluene in a state of relatively high purity which comprises reforming in the presence of dehydrogenation catalyst a prepared naphthene-containing charge substantially devoid of hydrocarbon materials boiling in the range of about 220-240 F., and distilling the reformate to recover a reformed products fraction boiling within about F. of toluene.

3. The method of reforming a naphtha charge for the recovery of a toluene distillate of enhanced purity from the reformate, which comprises distilling a naphtha fraction of suitable boiling range to separate out therefrom a middle out boiling approximately over the range of 220- 246 iii, the remainder of the naphtha fraction including hydrocarbons boiling above and below the range of the middle cut and containing naphthenic C7 hydrocarbons, subjecting to catalytic reforming at least a portion of said remainder substantially free from hydrocarbons boiling in the 229-2 10 F. range and containing said (37 hydrocarbons, and distilling the resulting reformate to separate out a toluene-contain ing distillate, said distillate being of enhanced toluene purity.

a. The method as defined in claim 3 wherein said catalytic reforming is effected in the presence of a noble metal catalyst.

55. The method as defined in claim 3 wherein said original naphtha fraction of suitable boiling range is one of high naphthene content and comprises Ce to C3 hydrocarbon components.

6. The method according to claim 5 wherein said catalytic reforming is effected under pressure conditions favorable for the conversion of Co napthenes to benzene, without significant production of coke.

7. The method according to claim 5 wherein said catalytic reforming is effected in the presence of a noble metal catalyst and at a total operating pressure of from about 250-400 pounds per square inch gauge.

8. The method as defined in claim 5 wherein said catalytic reforming is effected in the presence of a catalyst comprising 0.05 to 2% Pt on an alumina support composed of activated alumina which has been leached with a mild acid.

9. The method as defined in claim 5 wherein said catalytic reforming is efiected in the presence of a catalyst comprising 0.05 to 2% Pt on an alumina support composed of activated alumina which has been pretreated to incorporate 0.5 to 5% MgO therein.

ALEX G. OBLAD.

GEORGE ALEXANDER MILLS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,406,394 Newton Aug. 27, 1946 2,589,523 Woertz et al. Mar. 18, 1952 

1. THE METHOD OF CONVERTING C7 NAPHTHENES IN A NAPHTHA CHARGE TO TOULENE WITH THE SIMULTANEOUS PRODUCTION OF AT LEAST ONE AROMATIC HYDROCARBON COMPOUND FROM THE GROUP CONSISTING OF BENZENE AND XYLENES, WHICH METHOD COMPRISES: DISTILLING A NAPHTHA FRACTION OF SUITABLE BOILING RANGE TO REMOVE THEREFROM COMPONENTS BOILING WITHIN 10* F. OF TOLUENE, REFORMING THE REMAINING NAPHTHA UNDER DEHYDROGENATING CONDITIONS EFFECTIVE AT LEAST TO AROMATIZE METHYL CYCLOHEXANE, DISTILLING THE RESULTING REFORMATE AND RECOVERING A TOLUENE-CONTAINING DISTILLATE OF NARROW BOILING RANGE. 